Two government MPs, including Senator Bridget McKenzie, have joined calls to allow the rapid-fire Adler shotgun to be imported into Australia, just hours after Prime Minister Malcolm Turnbull declared the ban was "set in stone."

The calls come as the Liberal Democrats Senator pushing for the change, David Leyonhjelm, has urged Peta Credlin to "STFU" (shut the f--k up) after she rejected reports Tony Abbott did a deal that would allow the firearm into the country.

The issue escalated in Parliament this week when Senator Leyonhjelm said he would consider supporting the government's bills cracking down on unions in exchange for lifting the ban on Adler gun imports.

When the prime minister refused to rule out the prospect on Monday, Labor seized on the issue and suspended proceedings in the parliament, accusing Mr Turnbull of weakening Australia's tough and widely supported gun-control laws.

Mr Turnbull subsequently said the ban imposed under his predecessor Tony Abbott was permanent – unless amended. The ban will remain in place unless the states and territories strike an agreement about how to classify the gun and what sort of permit a gun-owner would require to use the weapon in Australia.

Late Tuesday, Troy Grant, the leader of the NSW Nationals Party and Minister for Police and Justice, told the ABC he would seek the state cabinet's support to free up imports by making gun owners state their purpose for owning the firearm.

Federal Nationals MPs Mark Coulton and Bridget McKenzie told Fairfax Media they supported the Adler shotgun being reclassified allowing it to be imported.

"It is the responsibility of the states and territories to classify and restricting its access as [Grant's] approach is a positive and common sense step," Senator McKenzie said.

Deputy speaker Mark Coulton said he knew of one gun dealer in his electorate of Parkes in New South Wales who had "hundreds" of guns on order and ready to import but was waiting on a final decision on the temporary ban.

"I'm hoping we can still get this through because I know of one gun dealer who has hundreds on order waiting for this decision," he said.

Mr Coulton said the Adler shotgun would primarily be used by farmers to shoot feral pigs on their properties and said he was horrified by Labor's attempt to cast firearms users as a safety threat.

"I think it's scandalous that the opposition is trying to make out that this is a gun-toting, security-threatening issue," he said.

Critically, Mr Coulton backed the answers provided by Prime Minister Malcolm Turnbull and Justice Minister Michael Keenan and said the real security risk came from the owners of illegal guns and not legally purchased and permitted weapons. He also hit out at Senator Leyonhjelm for making the issue headline news and said anyone genuinely interested in securing an outcome would be working behind the scenes.

"I'm disappointed that this has become a focus," he said.

"If you want to get something you usually gather the support on the quiet and do it behind the scenes, once it's headline news it becomes very difficult," he said.

This was also echoed by the Victorian Nationals backbencher Andrew Broad who said senators were in the house of review to examine legislation on its individual merits.

"Senators should review things on their merit," Mr Broad said.

He said he supported Australia's gun-control laws introduced amid great controversy by former Prime Minister John Howard but said in the two decades since, opponents had whipped up hysteria against legitimate firearm-owners.

"I'm very mindful of not denigrating people who responsibly use their guns," he said.

Under the Nationals Firearms Agreement, guns are placed into one of four categories: A, B, C or D depending on their capability. Guns in categories C and D are almost impossible to obtain in Australia while guns in category A are comparatively easier to acquire.

Anyone wanting a gun in category B has to state a specific purpose for wanting the weapon. There has been general disagreement about how the Adler gun should be classified because it can fire seven shot rounds.

In lieu of a consensus, the federal government imposed a 12-month outright ban on any Adler gun capable of firing more than five-shot rounds. That ban expired in August under a sunset clause the former Abbott government agreed to in a deal with Senator Leyonhjelm to secure his vote for a migration bill.

An email the senator released on Tuesday showed that under the deal, the ban would "automatically cease to be in place," once the one-year ban expired.

Despite his own willingness to barter on the issue, Mr Abbott lent his support to Labor by tweeting on Tuesday:

"Disturbing to see reports of horse-trading on gun laws. ABCC should be supported on its merits."

Mr Abbott's former chief of staff Peta Credlin claimed there was no deal during one of her paid appearances on Sky News.

"I want to say there was absolutely no deal between Tony Abbott and David Leyonhjelm in order to bring in the Adler shotgun," she said.

"Let's not forget we had gone through terror raid after terror raid and obviously Martin Place and Tony was adamant that it would not come into the country in the current classification that it was proposed for nor would it come in in the immediate aftermath of those arrest," she said.

Senator Leyonhjelm attacked Ms Credlin on Twitter.

"Conflating licensed firearms owners with terrorists. When you don't know what you are talking about you should STFU," he said.